// https://github.com/LinusU/encode-utf8
module.exports = function encodeUtf8 (input) {
    const result = []
    const size = input.length
  
    for (let index = 0; index < size; index++) {
      let point = input.charCodeAt(index)
  
      if (point >= 0xD800 && point <= 0xDBFF && size > index + 1) {
        const second = input.charCodeAt(index + 1)
  
        if (second >= 0xDC00 && second <= 0xDFFF) {
          // https://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
          point = (point - 0xD800) * 0x400 + second - 0xDC00 + 0x10000
          index += 1
        }
      }
  
      // US-ASCII
      if (point < 0x80) {
        result.push(point)
        continue
      }
  
      // 2-byte UTF-8
      if (point < 0x800) {
        result.push((point >> 6) | 192)
        result.push((point & 63) | 128)
        continue
      }
  
      // 3-byte UTF-8
      if (point < 0xD800 || (point >= 0xE000 && point < 0x10000)) {
        result.push((point >> 12) | 224)
        result.push(((point >> 6) & 63) | 128)
        result.push((point & 63) | 128)
        continue
      }
  
      // 4-byte UTF-8
      if (point >= 0x10000 && point <= 0x10FFFF) {
        result.push((point >> 18) | 240)
        result.push(((point >> 12) & 63) | 128)
        result.push(((point >> 6) & 63) | 128)
        result.push((point & 63) | 128)
        continue
      }
  
      // Invalid character
      result.push(0xEF, 0xBF, 0xBD)
    }
  
    return new Uint8Array(result).buffer
  }